An example of the conventional ultrasound probe in the field of inspecting a test object with ultrasound is disclosed in Patent Literature 1 cited below. This invention is structured with a gap, insulation layers, and electrodes formed on a silicon substrate. A damping material having substantially the same acoustic impedance as that of the silicon substrate is introduced into the opposite surface of the substrate. A DC voltage is applied between the electrodes and the silicon substrate so as to reduce the gap to a predetermined position. In this structure, an AC voltage is further applied in a manner contracting or expanding the gap in order to transmit ultrasound. The ultrasound probe also has the function of receiving the reflected ultrasound from the test object so as to detect a capacitance change between the electrodes and the silicon substrate. Here, the damping material plays the role of reducing ultrasonic wave reflection during transmission and reception. A specific damping material is prepared by mixing epoxy resin and tungsten particles in varying blending ratios, whereby the acoustic impedance of the material is adjusted to that of the silicon substrate.
Also, Patent Literature 2 cited below discloses an ultrasound probe having a piezoelectric element disposed on an acoustic backing with an acoustic impedance of 1.3 to 6 MRayls. The acoustic backing is described as a composite material mixed with zinc oxide fiber.
Furthermore, Patent Literature 3 cited below describes a CMUT (Capacitive Micromachined Ultrasonic Transducer) chip bonded with a backing to provide short pulses, i.e., a wideband ultrasonic waveform suitable for high-resolution use.